1. Field of the Invention
The present invention relates to a tooth for excavating, such as a bucket-tooth, ripper-point and the like for construction machinery. In particular, the present invention relates to a composite tooth, in which wear-resistance is selectively imparted to a part thereof required to have such property, for example a tip end.
2. Description of Related Arts
In construction machinery for excavating earth, such as a hydraulic shovel, bulldozer, or the like, a bucket tooth or a ripper point as shown in FIGS. 10 and 11 is temporarily mounted on the front end of a bucket and a ripper, respectively. Since this kind of bucket-tooth and ripper-point is subjected to severe friction and hence is seriously damaged by wear, they are generally constructed as replaceable parts. However, working efficiency is reduced, and hence the cost for parts are increased, when replacement is carried out frequently. Various improvements have therefore heretofore been devised so as to minimize replacements.
The first improvement is to enhance the wear-resistance of the mother material, i.e., the excavating tooth itself. The wear-resistance of the mother material is enhanced by means of hardening it. The toughness is however reduced to soften the material against impact. Wear-resistance can also be enhanced by adding an alloy element(s) to the mother material. Production cost is, however, considerably enhanced. In addition, when the mother material is to be produced by casting, there is a limit on the content of alloying elements, since casting becomes difficult when these elements exceed a certain limit.
The improvements which have been devised next are to selectively impart wear-resistance to a part of the mother material. The following methods are proposed as examples.
(A) A hole(s) is preliminarily formed on the mother material. It is then set in a mold. Molten metal with high wear-resistance is then poured into the hole(s) of the mother material set in a mold (Japanese Unexamined Patent Publication No. 49-86223). Metallic material having high wear-resistance is surface-welded on the mother material having good weldability (Japanese Unexamined Patent Publication No. 53-100603).
(B) An inserting hole(s) is preliminarily formed on the mother material, and, then a tip(s) of cemented carbide having high wear-resistance is embedded in the insert hole(s) (Japanese Unexamined Utility Model Publication No.49-5202, U.S. Pat. No. 805423, and Japanese Unexamined Patent Publications Nos.5452301, and 62-99527).
(C) A plurality of blank materials, each with different compositions, are successively laminated and integrally bonded with one another (Japanese Unexamined Utility Model Publication No. 51-69041 and Japanese Unexamined Patent Publication No. 56-122436).
(D) Particles or pieces of cemented carbide are insert-cast in the tip end or as a whole of the excavating tooth, so that the particles and the like are dispersed in the cast iron or steel (Japanese Unexamined Patent Publication Nos. 57-2804 and 54-75801, and Japanese Unexamined Utility Model Publication No. 61-190353).
(E) A preliminarily shaped, wear-resistant member is located in a mold. The mother material is then melted and poured around the wear-resistant member so as to insert-cast the latter in the former. The wear-resistant member is located in the mold in such a manner that at least a part of the member is exposed on the surface of the mother material (Japanese Examined Utility Model Publication No. 62-15336, and Japanese Unexamined Patent Publication No. 59-218255).
The excavating tooth produced by the pouring or surface-welding of item (A) and by the embedding of item (B) exhibit poor adhesion between the mother material and wear-resistant material. The wear-resistant material falls down during use of the excavating tooth.
In order to produce the excavating tooth by lamination and bonding by item (C) above, many man hours are required, and heat treatment is necessary for relieving welding stress and the like.
Regarding the excavating tooth produced by insert-casting the wear-resistant material in a dispersed state as is referred to in item (D), above, the particles and the like of cemented carbide are exposed and easily separated from the tooth, as it is worn out with use. The properties of cemented carbide particles embedded thus therefore cannot be taken advantage of.
Regarding the excavating tooth, in which the wear-resistant material is insert-cast and is exposed on the surface as is referred to in item (E), above, since the cooling speed of the melt of cast mother material is different between the surface and center, fusion bonding between the mother material and the wear-resistant material becomes poor, and further, the wear-resistant material is liable to crack due to thermal expansion and shrinkage. Particularly, in Japanese Unexamined Patent Publication No. 59-218255, the wear-resistant material in the form of a rod is embedded in a direction perpendicular to the longitudinal direction of the excavating tooth. The wear-resistant material is therefore subjected to bending force under excavation. There is hence danger that the material may be broken. In addition, when the tip end is worn down beyond a certain point, the rod protrudes at the tip end and is suspended or falls down. In Japanese Examined Utility Model Publication No. 62-15336, the embedded wear-resistant members are provided with a plurality of extensions which are elongated from a central wear-resistant member in upper and lower directions or from an upper wear-resistant member in a lower direction. If the difference in the wear-resistance between the wear-resistant material and mother material in this excavating tooth is very great, only the wear-resistant material is left not worn out and forms unevenesses on the tip end along the width of the tooth. In this state, the excavating resistance is increased, and, the convex parts, which are left not worn out, are subjected to bending and may be broken.